1. Field of the Invention
The present invention relates to a heat insulator apparatus for use in a vehicle floor which prevents the heat of an exhaust part from being transmitted to the vehicle floor.
2. Description of the Related Art
As a technique for preventing the heat of an exhaust part against transmission to the vehicle floor, for example, there is known a heat insulator for a vehicle which is disclosed in JP-A-9-175198. In the present heat insulator for a vehicle shown in FIG. 6, an outer heat insulating plate 1 is mounted below a floor 4 to form a gap G1, and an inner heat insulating plate 2 is mounted below the outer heat insulating plate 1 to form a gap G2. That is, provision of the gaps G1, G2 can enhance the heat insulating effect to thereby be able to increase the effect of insulation of the heat from an exhaust pipe 3 to the floor 4.
Also, during the running time of the vehicle, the air flows into the gaps G1, G2 to thereby carry out a cooling action, which can further enhance the heat insulating effect. In this manner, use of the heat insulator for a vehicle can shorten the distance between the floor and engine exhaust pipe system, which makes it possible to expand the freedom of the layout of the vehicle.
However, in the case of the above-mentioned conventional heat insulator for a vehicle, at the time when the vehicle stops after it has run once, the hot air within the gap G2 is easy to move upwardly from the front and rear edges of the outer heat insulating plate 1, so that the temperature of the floor is easy to rise.
Also, although the exhaust pipe 3 is cooled by the vehicle running wind that is drawn into the vehicle while the vehicle is running, the air, which has absorbed the heat of the exhaust pipe 3 and thus become hot, reaches directly to the floor from the rear ends of the outer and inner heat insulating plates 1 and 2 to thereby heat the floor, so that the temperature of the floor is easy to rise.
The present invention aims at eliminating the drawbacks found in the above-mentioned conventional heat insulator. Accordingly, it is an object of the invention to provide a heat insulator apparatus for a vehicle floor which, when a vehicle stops after it has run as well as while the vehicle is running, can enhance the heat insulating effect.
In attaining the above object, according to a first aspect of the invention, there is provided a heat insulator apparatus for a vehicle floor, wherein there are formed gaps each between the mutually adjoining ones of a plurality of heat insulating plates to thereby form air passages therebetween and these heat insulating plates are, as a group, interposed between a vehicle floor and an exhaust part disposed below the vehicle floor to thereby prevent the heat of the exhaust pipe from being transmitted to the vehicle floor, wherein the air entrance portion of at least one of the air passages is narrowed.
Since at least one of the air passages is narrowed in the air entrance portion thereof, in the vehicle stopping time after running, the air within the air passage lingers within the air passage to thereby secure the heat insulating characteristic of the air passage. Therefore, even in the vehicle stopping time after running, the heat insulator apparatus for a vehicle floor can provide a heat insulating effect.
Also, according to a second aspect of the invention, in a heat insulator apparatus for a vehicle floor as set forth in the first aspect, the heat insulating plates not only enclose the exhaust part but also are extended by a predetermined distance backwardly from the exit portion of the exhaust part.
In the vehicle running time, a running wind, the temperature of which has been raised due to heat radiated from the exhaust part, flows backwardly of the exhaust part and rises upwardly. Extension of the heat insulating plates by a predetermined distance backwardly of the exit portion of the exhaust part can prevent the transmission of the heat of the high-temperature running wind flowing backwardly of the exhaust part. Therefore, in the vehicle running time, the heat insulating effect can be enhanced.